During the operation of motor vehicle generators sudden surge voltages occur in response to a load dump because the magnetomotive force and the stored magnetic energy of the field coil of the generator can only be degraded at a finite rate. In common generator control circuits the field coil of a generator is de-energized by means of expensive components, such as power zener diodes, in order to prevent the output voltage of the generator to increase to high values which may cause damage to various electric components connected to the generator.
Various circuits for de-energizing field coils in order to reduce the magnetic energy stored therein are known in the art. Although such circuits may alleviate the problem of surge voltages that may occur especially in response to a load dump, there is still the need for improved circuits that allow a quick and reliable de-energization of field coils.